The demand for location based services continues to increase. There are many techniques for determining the position of a device using radio signals. Technologies such as Global Positioning Systems (GPS) are often used in outdoor environments. Indoor location sensing presents different problems than outdoor positioning. Conventional techniques have difficulty accurately calculating indoor locations in high ceiling areas or multi-story areas comprising open atriums, stairways, or escalators.
Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.